Representing Sheared Convective Boundary Layer by Zeroth- and First-Order-Jump Mixed-Layer Models: Large-Eddy Simulation Verification

摘要

Dry convective boundary layers characterized by a significant wind shear on the surface and at the inversion are studied by means of the mixed-layer theory. Two different representations of the entrainment zone, each of which has a different closure of the entrainment heat flux, are considered. The simpler of the two is based on a sharp discontinuity at the inversion (zeroth-order jump), whereas the second one prescribes a finite depth of the inversion zone (first-order jump). Large-eddy simulation data are used to provide the initial conditions for the mixed-layer models, and to verify their results. Two different atmospheric boundary layers with different stratification in the free atmosphere are analyzed. It is shown that, despite the simplicityof the zeroth-order-jump model, it provides similar results to the first-order-jump model and can reproduce the evolution of the mixed-layer variables obtained by the large-eddy simulations in sheared convective boundary layers. The mixed-layer model with both closures compares better with the large-eddy simulation results in the atmospheric boundary layer characterized by a moderate wind shear and a weak temperature inversion. These results can be used to represent the flux of momentum, heat, and other scalars at the entrainment zone in general circulation or chemistry transport models.